Sweedler notation

Summary

Sweedler notation is a shorthand for the comultiplication of a coalgebra: one writes $\Delta(c) = \sum c_{(1)} \otimes c_{(2)}$, or even $c_{(1)} \otimes c_{(2)}$, without naming the terms of the sum. Coassociativity lets one write iterated coproducts as $c_{(1)} \otimes c_{(2)} \otimes c_{(3)}$ without brackets. It is named after Moss Sweedler and is the standard notation for computations with Hopf algebras and comodules.